Electronic control module for detonator

ABSTRACT

Electronic control module for a detonator comprising a printed circuit board ( 1 ) equipped with components of the circuit, enclosed in a tubular casing ( 12 ) embedded in a blocking resin ( 15 ) of the board in the casing, wherein a shielding screen ( 3 ) is interposed between the board ( 1 ) and the tubular casing ( 12 ), which screen has an insulating face turned towards the casing ( 12 ) and a conductive face ( 6 ) turned towards the board, the conductive face being electrically connected to the earth wire of the printed circuit board ( 1 ).

The present invention relates to an electronic control module for a detonator, used in mines and quarries and forming the priming system of explosives.

A detonator module generally comprises a printed circuit board carrying the electronic components of the circuit, which board has the shape of an elongated card accommodated in a section of tubing and embedded in this section or tubular casing by a blocking resin. From one of the ends of the casing extend conductors for connecting the module to a firing line, which in turn is connected to a central programming and control unit, whereas at its other end the casing and the printed circuit board that it contains has means for connecting it to the pyrotechnical primer that is added to it.

These electronic detonators are used in a hostile environment. It is necessary, therefore, to protect the components of the electronic module as much as possible on the one hand against mechanical stresses resulting from the shock waves coming from the explosions of preceding charges in a programmed firing plan and from electromagnetic stresses that can perturb the communications between the module and the central programming and firing control unit.

To withstand mechanical stresses, generally a strong metal casing of steel is chosen. However, this has drawbacks: on the one hand inopportune electrical contacts may occur between the electronic components of the module and the casing, and on the other hand this casing transmits and concentrates all the electromagnetic perturbations that may come from the outside environment onto the electronic circuits.

To remedy these drawbacks, it is the object of the invention to provide an electronic module for a detonator comprising a printed circuit board equipped with components of the circuit, which is enclosed in a tubular casing and is embedded in a blocking resin of the board in the casing, wherein a shielding screen is interposed between the board and the tubular casing, which screen has an insulating face turned towards the casing and a conductive face turned towards the board, the conductive face being electrically connected to the earth wire of the printed circuit board.

This screen thus ensures a double function, i.e. an insulation against inopportune electrical contacts that may occur between the components of the electronic circuit of the module and the outside casing and a screen for electromagnetic perturbations coming from the outside environment and transmitted or concentrated by the ferromagnetic metal casing.

In an advantageous embodiment of this screen, the screen is formed by a sheet of flexible and elastic plastic material, the conductive face of which is covered with a conductive ink, except for a peripheral margin. This sheet can thus be easily connected electrically to the printed circuit board and be wound around this board with a large overlap, the elasticity of the sheet making it possible to easily insert it into the metal casing by rolling it up with a diameter smaller than the inside diameter of this casing and, once inserted in the casing, the sheet tends to unroll elastically and comes to rest against the inside surface of the tubular casing, thus forming a provisional holding means of the electronic board before it is cast with the blocking resin.

Other characteristics and advantages of the invention will become apparent from the description given below of an exemplified embodiment.

Reference will be made to the attached drawings, wherein:

FIG. 1 illustrates the printed circuit board of the electronic module according to the invention, equipped with its shielding screen,

FIG. 2 shows a front view of just the shielding screen,

FIG. 3 illustrates the inserting of the electronic circuit board with its shielding screen into a ferromagnetic casing, and

FIG. 4 illustrates in longitudinal section the produced electronic module.

FIG. 1 shows a printed circuit board 1 in the form of an elongated card that carries the electronic components required for the functioning of the control module of an electronic detonator and, in particular, a capacitor 2 which forms an energy reserve intended to be charged prior to the firing and to be discharged into the pyrotechnical primer that will be connected to the electronic module. The shielding screen according to the invention carries the reference numeral 3 in FIG. 1 and is shown as a rigid sheet but can be elastically bent over itself, having the consistency of a sheet of RHODOID or a photographic film. This screen 3 is mounted roughly perpendicularly to the board 1 by means of connection tabs 4.

From FIG. 2 it can be noted that this screen 3 comprises a base foil 5 of an insulating plastic material having the consistency described above, on one face of which a print 6 of conductive ink is provided. The ink does not cover one of the faces of the sheet of plastic material 5 completely: it leaves a peripheral margin 7 unprinted. The face covered with ink is in turn covered with an insulating film 8, which has two bottom reserves 9 and 10 where the tabs 4 of conductive material are fastened so that they are in electrical contact with the conductive ink 6. These tabs 4 have parts that project outside an edge of the sheet 5, which projecting parts can be placed in openings of the printed circuit board 1, which conductive openings are connected to the earthing circuit of this printed circuit board.

During the mechanical electrical assembly of the screen 3 and printed circuit board 1, the sheet 3 is rolled up enclosing the printed circuit board 1, as illustrated in FIG. 3. The face of this screen coated with conductive ink is turned towards the board 1. The size of the screen 3 perpendicular to the board 1 is such that it can be rolled up with an overlap zone 11 so as to form a complete screen in the radial direction between the components carried on the printed circuit board and the outside.

Having taking the trouble to roll up the screen to form a tube with a diameter smaller than the inside diameter of a metal casing tube 12, it is easy to insert the board 1 and rolled up screen 3 into the inside of the metal tube 12, and when one lets go off the screen 3 after inserting it, the screen tends to unroll and flattens itself against the inside surface of the metal tube 12. The printed circuit board 1 is then provisionally held in place inside the metal tube by the friction between the screen 3 and this tube. It will have been noted that the margin 7 ensures that the conductive ink will not come into contact with the metal tube 12.

This metal tube will preferably be a seamless steel tube.

FIG. 4 shows the elements that have already been described with, for the printed circuit board 1, an electrical conductor 13 soldered onto the printed circuit board and coming out of one of the ends of the metal tube for connecting the module to the programming and control unit. The metal tube 12 has been closed by a plug 14, passed through in a tight manner by the conductor 13, so as to be able to fill the tube equipped with the printed circuit board and the screen practically completely with a blocking resin 15, preferably a polyurethane resin so as to ensure inside the tube 12 a resilient holding in position of the printed circuit board 1 and its components, that can better take the shock waves.

Finally, it will have been noted that FIG. 4 comprises a capacitor 2 surrounded by a casing 16 made of natural or synthetic rubber foam, forming a shock-absorption and damping element of the accelerations of the condenser 2 under the effect of the shock waves. In fact, these capacitors are electro-chemical condensers that are sensitive to mechanical shocks and can lose all or part of their charge under the effect of a very great acceleration as is caused by a shock wave.

It will furthermore be understood that the casting of the polyurethane resin can take place easily since the tube is held vertically, which position is made possible by the holding in position without sliding of the printed circuit board inside the tube 12 by means of the elastic screen. 

1. Electronic control module for a detonator comprising a printed circuit board (1) equipped with components of the circuit, which is enclosed in a tubular casing (12) and is embedded in a blocking resin (15) held inside the casing, wherein it comprises a shielding screen (3) interposed between the board (1) and the tubular casing (12), provided with an insulating face turned towards the casing (12) and a conductive face (6) turned towards the board, the conductive face being electrically connected to the earth wire of the printed circuit board (1).
 2. Module according to claim 1, wherein the shielding screen (3) is formed by a sheet of flexible and elastic plastic material (5), the conductive face of which is covered with a conductive ink (6) except for a peripheral margin (7).
 3. Module according to claim 2, wherein the layer of conductive ink (6) is covered by an insulating protection film (8).
 4. Module according to claim 1, wherein the tubular casing (12) is formed by a section of seamless steel tubing and in that the blocking resin (15) is a polyurethane resin.
 5. Module according to claim 1, comprising in the known manner an electrochemnical capacitive component (2), wherein this component (2) has an outside shock absorption casing (16). 